1. Field of the Invention
The present invention relates to a high-pressure pump for feeding fuel to an internal combustion engine, and more particularly to such a high-pressure piston pump for feeding fuel to a common rail of an internal combustion engine.
2. Description of the Prior Art
A piston pump of the type with which this invention is concerned generally comprises a pump housing in which a fuel feeding duct, at least one cylinder connected to the feeding duct and one delivery duct are made. The piston pump comprises a reciprocating mobile piston within the cylinder and a check valve, which allows the fuel flow when the pressure in the cylinder reaches a level capable of exerting a force on the valve element or ball higher than the sum of the force exerted by the fuel pressure within the delivery duct downstream of the check valve and of the force of opposing spring acting on the valve element.
Generally, the check valve used in this type of high-pressure pumps extends along a given axis, is arranged along the delivery duct and comprises a seat; a mobile valve element within the seat; and a biasing and guiding assembly, which comprises a fastening member suitable to be fastened to the pump housing and to close the seat in fluid-tight manner, and a helical compression spring adapted to exert a closing bias on the valve element.
The different functional needs thus require the valve element to be made of harder material than the spring, which in turn is made of harder material than the fastening member. If to this fact it is added that the helical spring, when compressed, is subjected to axial bending or deflection, which, in turn, produces rotations of the spring about its longitudinal axis, it results that the spring wearing the fastening member and the ball wearing the spring. The higher the fuel flow rates, the higher and more marked the wear phenomena, that determine, in time, dimensional variations and incorrect pump operation.
Regarding this, it is relevant to observe that common rail systems are increasingly installed in commercial vehicles (in trucks, off-highway vehicles) because also this type of engine must respect anti-pollution provisions. The high power of commercial vehicles entails that the fuel pumps must be capable of managing high flow rates which are the main cause of bending in the helical spring-valve system.